> ; / 1 1 r --1 rr1 : l iJ:i! i!i !J: 'Uì j!....: _ '1* !1 : I:' I II í'j . , ;,! ," . ;: ;ü iU I/ , lf l ' l ( ,N .' ,j . i ^ ,'1' )- ! :1 ::"l ",;:" - - >;;. ':";.. ...::;; -- . ':' : . i !; i-i.. . ':" "ì t .. , J ;,., " / <:?'-4 \J tt tJ I'!I: L . M il . <:/' I I d.. ; _mm . 1 ! ..........'" # . - - -- , 98 P HYSICS is often thought of as the paradigmatic science. After the discoveries of Newton, scien- tists recognized that the striking thing about physical theories is their power of prediction. For example, Newton's laws enable us, knowing the moon's position, to predict its position into the indefinite future. Biological laws ap- pear to have an altogether different character. Living things have evolved through a mixture of chance and ne- cessity, and are the result of processes that are essentially beyond prediction. If an extraterrestrial biologist armed with every scientific tool we can imag- ine had been around when life began on Earth, he could not have predicted the future existence of a zebra-to say nothing of a human being, or even a blade of grass. In physics, we deal with what have been characterized as "limiting cases" -situations that can be so highly idealized and simplified that they can be subjected to predictive law . We can talk about "the" elec- tron, because each electron is like ev- ery other electron. But since no two living things are exactly alike biologi- cal laws are statistical, and since bio- logical systems are so complex the -'-'I t 'q r ,i i ' -:,..J t id ":1' i .(' ;: ,-: ::-- -- ' ..<<<'-.. ...... '<o'Io -Ao.*........ll t ::': j .....,. ' I ' AJ "' '. ........ . "" ....... '. .... .. .. ""'._' . . . >t << ogy-is given only a few pages. Of the history of research on the brain, there is essentially no mention.) What the reader will find is a marvellous course in evolution, taught historical- ly. For a reader who is willing to make the effort, this book provides one of the best and most nearly complete discussions of these ideas to be found anywhere. It is an example of those rare books in popular science which can teach scientists as well as laymen. Professor Mayr devotes most of a chapter at the beginning of his book to a discussion of the distinction between mathematical physics and evolutionary biology. He writes, "There are some sciences, like the physical sciences and much of functional biology, in which quantification and other mathe- matical approaches have a high explan- atory or heuristic value. There are oth- er sciences, like systematics and much of evolutionary biology, in which the contributions of mathematics are very minor." Indeed, as he goes on to point out, there are important historical ex- amples in which the undervaluing of biological evidence has got physicists into trouble. For example, in the nine- teenth century the great British physi- cist William Thomson- later Lord Kelvin-made a calculation of the age of the earth based on a simplified model that held that the earth had cooled contin- uously since it was formed. He concluded that the earth could not be more than twenty-four million years old, and that Dar- win, who on biological and geological evidence had es- timated the age of the earth at more than a billion '> -, years, must simply have been wrong. Professor Mayr remarks, "It is rather amusing with what assurance Kelvin assumed the correctness of his own and the error of the natu- ralists, age determinations. Since biology was an infe- rior science there could be no question where the er- ., ror was. Kelvin never al- lowed for the possibility of the existence of an un- known physical factor that would eventually validate BOOKS T he Evolution of Evolution laws are usually nonpredictive. This makes biology a science with goals, methods, and a philosophy very differ- ent from those of physics. Ernst Mayr, the Alexander Agassiz Professor of Zoology, Emeritus, at Harvard, is a master of modern biol- ogy. He is one of the people who helped to synthesize evolution and ge- netics-a synthesis that seems clear now that so much is known about the workings of the gene, but was origi- nally far from obvious. Professor Mayr has written a monumental his- tory of biological ideas, "The Growth of Biological Thought'" (Harvard; $30). The book is the result of ten years of specific preparation and a life- time of experience as a working bi- ologist. It is nine hundred and sev- enty-four pages long, and includes six- ty-two pages of references. It is not a full-scale history of biology-an en- terprise that would be essentially im- possible, certainly for anyone man, in the depth that Professor Mayr is striv- ing for. (It contains nothing, for example, about the development of biological thought in the Orient. The modern attempt at a mathematical theory of animal behavior-sociobiol- - "'i - :'" -...................! df rd J: l ,. r- -""""- fl r'- : t{ ! i F !y! t . if F I, Á I rt:J c:.' , ""=Ii. t ' 1 , 'f .;: N< = i ( <<< --::. i "\" '> ( "T he talks are in a delicate stage." .!$. ':::; :::.,t( \' ." -*-+"" ;. ::=:-.